In the side airbag device illustrated in following Patent Document 1, the interior of an airbag is sectioned in the vertical direction into three inflating portions (chambers), and an inner bag, that contains an inflator, is provided within the central inflating portion. The inner bag communicates with the upper inflating portion and the lower inflating portion through upper and lower openings, and communicates with the central inflating portion through an intermediate opening. Moreover, this inner bag is disposed such that, in the inflated and expanded state, the front end of the inner bag is positioned further toward the rear than the front end of the central inflating portion and further toward the front than the front end of a seat bag.
In the side airbag device of the above-described structure, gas for inflation that is jetted-out from the inflator is first supplied to the inner bag, and the inner bag expands. The gas for inflation that is within the inner bag flows from the upper opening of the inner bag into the upper inflating portion, and flows from the lower opening into the lower inflating portion, and flows from the central opening portion to the central inflating portion. Due thereto, the respective inflating portions inflate, and from the shoulder portion to the lumbar region of the passenger is restrained by the corresponding inflating portions of the airbag.
Further, the inner bag is disposed such that the front end of the inner bag is positioned as described above. Therefore, at the time of inflation and expansion of the airbag, due to the inner bag inflating in a vicinity of the side of the passenger, the passenger is restrained not only by the airbag (the main bag), but also by the inner bag (the internal bag). Due thereto, the restraining performance is improved.